After good king Jotham, Judah gets bad king Ahaz. He's bad out of the box and never gets better. How bad is he? Let's just say that, in addition to the standard issue idolatries, he makes his sons "pass through fire" which may be code for child sacrifice.
YHWH uses foreigners and infidels to punish Judah under Ahaz. The Judahites suffer defeat by Aramean and Israelite invaders. The infidels prove more faithful than the Davidic king. At the word of a prophet named Oded they release their captives and return their plunder. Jesus' parable of the Good Samaritan (Luke 10:35 ff.) may be based partly on the Israelites treatment of their Judahite relatives.
Under threat from Edomite armies, Ahaz pays tribute to Assyria for protection but receives no help. Taking the wrong lesson from all of this, Ahaz turns to the gods of Aram. He closes YHWH's temple and builds altars on every street corner.
Upon Ahaz's death, his son Hezekiah takes the throne. If, in the Chronicler's estimation, Ahaz was judah's worst king, Hezekiah is the best. In comparison to the parallel aacount in 2 Kings, The Chronicler puts more emphasis on Hezekiah's religious reforms and less stress on the Assyrian invasion. Hezekiah compares well to David and Solomon. Details of Hezekiah's story echo the accounts of those earlier monarchs.
In 2 Chronicles 29 Hezekiah makes short work of reopening YHWH's temple. In chapter 30 he invites all Israel, including the remnants of the now vanquished northern kingdom to a Passover festival. The celebration is held a month late, a concession permitted in Numbers 9:9-11. The king prays for the northerners who participate in the festival without being consecrated. YHWH "heals" them--an interesting turn of phrase. By common consent the featival runs an extra week.
In a sense "all Israel" (or all that is left) is reunited under Hezekiah.
Hezekiah reestablishes regular worship in the temple. In chapter 31 Hezekiah rids "all Israel," north and south, of idols. A superabundance of tithes and offerings come in. The priests and Levites are well provided for.
Next: 2 Chronicles 32-34